Potentiometer



Aug. 26, 1969 7 5. R. LAWSON 3,464,050

POTENTIOMETER Filed Dec. 20, 1967 2 Sheets-Sheet 1 mvau'rov. Guam:- 0.- LAwsou n'r-romueyi Aug. 26, 1969 G. R. LAWSON 3,464,050

' POTENTIOHETER File d Dec. 20, 1967 2 Sheets-Sheet 2 26; 26:, \J m in loos-1454521 1 9,-. 0 on I l 1 a la 2' I 149 I auvw'ron.

Bus? Q. Lawson United States Patent 3,464,050 POTENTIOMETER Gustaf R. Lawson, Somerset, N.J., assignor to Circle F Industries, Inc., a corporation of New Jersey Continuation-impart of application Ser. No. 647,101, June 19, 1967. This application Dec. 20, 1967, Ser.

Int. Cl. H01c 5/00 US. Cl. 338-89 9 Claims ABSTRACT OF THE DISCLOSURE A potentiometer particularly for incorporation in phase shift circuitry to control current flow during both halfwaves of an alternating current cycle. A single, continuous, unidirectional operation of the-potentiometer adjusts the phase angles of both half-waves consecutively. Abutting high and low resistance surfaces are moved conjointly in respect to a series of contacts. Assuming a starting position at full off, a unidirectional shift of the abutting surfaces in respect to the contacts first adjusts the phase angle of one half-wave from a non-conducting current condition until there is conduction for substantially the full duration thereof, and thereafter adjusts the angle of the other half-wave correspondingly until, ultimately, there is current conduction over the duration of the fullwave.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 647,101, filed June 19, 1967.

BACKGROUND OF THE INVENTION Field of the invention The invention pertains to the variable control the alternating current waveform, through the provision of a potentiometer or variable resistance that would be most usually (though not necessarily) manually operated by a control knob or handle.

Description of the prior art Discussion of potentiometers made according to the prior art, as well as discussion of the present invention, will be directed principally toward devices of this type as employed in continuously variable lamp dimming or motor speed control circuits having therein phase shifters operating upon bidirectional solid state switching devices such as triacs and quadracs. It will be understood, however, that this is only for the purpose of promoting clarity of understanding of the invention, and should in no sense be taken as limiting in nature.

In any event, the potentiometers used in the prior art in circuits of the type described are so designed that assuming the resistance to be at its maximum value, lowering said value to a point Where conduction begins causes power to come on at a minimum value simultaneously, and to the same extent, during both half-waves of a single cycle of alternating current. As the resistance is progressively lowered from this minimum on setting, the minimum angle appearing in both halves of the wave form is progressively increased, simultaneously and to the same extent, until the full on position is reached.

A potentiometer as described above has certain undesirable characteristics. One is that the phase shift circuit in which the potentiometer is incorporated suffers from Patented Aug. 26, 1969 the hysteresis effect. Thus, if the potentiometer resistance is increased to a point where, for example, an associated solid state bidirectional switch never conducts and then is gradually decreased, a point is reached where said switch jumps on to a certain power output level. This may be termed a minimum on power output level. From this level, the-resistance might be progressively decreased, so that there is corresponding increase in the power supplied to the lamp, motor, or other device controlled.

Alternatively, it is possible to decrease the power output level from the minimum on condition thereof, by increasing the resistance. In the prior art, it is possible to lower the power output level from the minimum on position in this way, for a time. However, if the resistance is increased to a point where the solid state switch stops conducting, or if the main power supply should be even momentarily interrupted, then the switch must once more be turned on to its minimum on level before it can be set to a lower power level.

Another undesirable characteristic which has been noted in connection with potentiometers made according to the prior art resides in the lack of stability of circuits incorpo'rating said potentiometers at low power outputs, producing a tendency to amplify line voltage variation. Thus, as the voltage drops, the power output voltage level also drops and in addition the firing phase angle increases thereby further decreasing the power output. This can be considered as a characteristic of voltage change amplification.

SUMMARY OF THE INVENTION The present invention was developed to eliminate the hysteresis effect, and at the same time reduce significantly the characteristic of voltage change amplification.

To this end, I have devised a potentiometer incorporating a base of electrical insulation, on which there are abutting, elongated surfaces, one a high-resistance surface and the other a low-resistance surface. These abut end to end, and in one form of the invention the base is circular and is rotatable by the user through the provision of an attached knob. The surfaces are coated or otherwise provided upon the base, extending along the peripheral area thereof. In a preferred embodiment, the high and low resistance surfaces are of equal length, each extending through substantially 180' along the marginal area of the base.

A common line contact is in wiping engagement with the surfaces mentioned above, and also in wiping engagement with said surfaces is a pair of load contacts, angularly spaced from the line of contact at opposite sides thereof.

In a variation of this arrangement, the base may have rectilinear rather than rotary motion, with the high and low resistance surfaces abutting end to end along the fine of movement of the base and with the contacts equidistantly spaced along said line.

In either arrangement, conduction begins to occur as the resistance is lowered, at the same minimum value or phase angle as is found in circuits employing potentiometers according to the prior art. However, in the invention the minimum angle is found only in one half-wave, so that the minimum on power level is only 50% of that which obtains when the prior art potentiometers are employed. The angle in each half-Wave is controlled independently, reducing the voltage amplification effect by more than 50% as found through actual measurements and eliminating hysteresis completely.

3 BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a perspective view of a potentiometer according to the present invention, designed for rotary operation;

FIGURE 2 is a view similar to FIGURE 1, showing a modified form in which the potentiometer is adapted for multiple circuit control;

FIGURES 3-7 are diagrammatic representations of a potentiometer or variable resistaance according to the present invention, with the position of the parts progressing from a full off position seen in FIGURE 3, to a full on" position seen in FIGURE 7;

FIGURE 8 is a chart illustrating the waveform of the alternating current cycle as developed by progressive adjustment of the potentiometer from its FIGURE 3 to its FIGURE 7 position;

FIGURE 9 is a view of a waveform according to the prior art, shown at its minimum on setting; and

FIGURES 10-14 are somewhat diagrammatic illustrations of a modified form of potentiometer wherein the operation is in a straight line rather than by rotary motion, the modified potentiometer being illustrated in positions corresponding to those shown in FIGURES 3-7 for the rotary type.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGURE 1, I have illustrated, in simplified, somewhat diagramatic form, a potentiometer according to the present invention, designed for rotary operation. This, I believe, would be the type generally employed, although as will presently appear it is quite possible to carry out the inventive concept by a potentiometer having rectilinear rather than rotary motion.

In any event, in FIGURE 1, I have illustrated a base 10 which is formed of a hard, electrically insulating material such as a thermosetting phenolic resin, electrical fiber, or the like. Base 10 is secured at' its center to an operating shaft 12, which can project exteriorly of the housing (not shown) in which the base would be normally confined, and outside said housing the shaft would have connected thereto a turn knob 14 accessible to a user.

The invention includes a high resistance surface 16 and a low resistance surface 18. These can be coated upon the base, or alternatively, they could be preformed strips adhesively or otherwise secured to the surface of the' base.

Surface 16 offers a high degree of electrical resistance to the pass-age of an electrical current therethrough, while surface 18 is a current carrying material that would offer a minimum resistance, so that there is essentially free conduction through the surface 18. Thus, the surfaces 16, 18 respectively may be considered as being high and low resistance paths through which electrical current flows during use of the potentiometer.

As will be observed, the paths 16, 18, abut end to end at a meeting line 20, with each path extending through substantially 180". At the ends of the paths remote from line 20, a small gap 22 is provided, across which electrical current of the maximum voltage for which the potentiometer is rated, is not permitted to flow.

Angularly spaced 90 apart about the base are contacts 24, 26, 28. Contact 28 in a typical phase shift circuit in which the potentiometer would be used, is a line contact common to the respective load contacts 24, 26.

Referring now to FIGURES 37, in FIGURE 3 the potentiometer is shown in its position offering maximum resistance to the passage of electrical current therethrough, which position may be termed the full off position. Referring to FIGURE 8, the uppermost illustration of the waveform (which actually, signifies no wave at all) corresponds to the FIGURE 3 potentiometer position.

It will be observed at this point that assuming the device to be connected in a pair of phase shift circuits one of which controls flow during the negative and the other of which controls flow during the positive half-wave, con- 4 tacts 24, 28 connect the invention in the positive half-wave control circuit, and contacts 26, 28 connect the potentiometer in the negative half-wave control circuit.

The associated phase shift circuitry is not illustrated because the present application is concerned with the potentiometer per se. Typical circuitry of this type will be found in parent application Ser. No. 647,101 filed June 19, 1967.

As seen from FIGURE 3, in the full ofi condition half the length of the high resistance paths 16 extends between contacts 24, 28 while the other half of said length extends between contacts 26, 28. Therefore, current flow in both half-wave control circuits encounters maximum resistance, to the point that to all intents and purpose, the controlled appliance is turned completely off.

To facilitate an understanding of the operation, I have shown in association with the potentiometer illustrations of FIGURES 3-7, and also in the chart of FIGURE 8, a scale the opposite ends of which have been designated off and on. The scale would not be displayed in a commercial device in which the potentiometer is incorporated, more than likely, since it shows steps or definite gradations of power when in fact the power is infinitely variable. A scale could be provided, however, if the manufacturer so desires.

In any event, the scale extends through substantially being coextensive with the high resistance path 16 when the potentiometer is in its full oif position shown in FIGURE 3. Under these circumstances, one end of said path is in registration with the off point of the scale, while the notation on of the scale is in registration with the other end of said path.

The scale has been marked with arbitrary values through 10 having no significance other than to identify the divisions of the scale.

If, now, the potentiometer is rotated slightly from its FIGURE 3 to its FIGURE 4 position, to locate, adjacent point 1 of the scale, the end of the high resistance path that was in registration with the off point on the scale, the phase angle of the positive half-wave will be as shown in the minimum on waveform illustration of FIGURE 8, at a value designated by the numeral 1 in the corresponding scale shown in the chart of FIGURE 8.

Referring now to FIGURE 9, showing a waveform designated minimum on as developed by the potentiometers of the prior art, it will immediately be observed that the minimum on setting produced by the prior art devices is double that developed by use of a potentiometer according to the present invention, in terms of the power output level developed in the appliance control circuitry. If one were to now turn the prior art potentiometer back to increase the resistance, one could lower the power output level to perhaps 50% of the minimum on level shown in FIGURE 9. Thereafter, however, if the device is turned off while at a power setting below minimum on, it would not come back on unless one were to then once again lower the resistance. The appliance would now come on only if the potentiometer is at or above the minimum on setting shown in FIGURE 9, which is considerably higher than the setting at which the appliance went off. This is the hysteresis effect, and it is avoided by my potentiometer, which produces a waveform such as shown in FIGURE 8 as the minimum on waveform.

FIGURE 8, in the waveform designated minimum on, shows the power output level at its full minimum, that is, any increase in the resistance above the minimum on resistance value would turn the appliance off. Thereafter, when the appliance is again turned on by moving the resistance from its FIGURE 3 off position to its FIGURE 4 minimum on position, the appliance come on at the same lowest power output level at which it went off previously.

It may be observed, in this regard, that when the potentiometer is rotated to its FIGURE 4 position, there is still only high resistance material between contacts 26, 28, so that there is still a complete absence of conduction,

practically speaking, during the negative half-wave of the cycle.

It may also be observed from FIGURE 4 that the reason for developing the minimum on phase angle in the positive half-wave is that the angular distance between contacts 24 and 28 is now composed almost entirely of a high resistance path, but is also composed slightly of a path of low resistance material.

Referring now to FIGURE 5, continued rotation of the potentiometer in a clockwise direction viewing the same as in FIGURES 3-7, ultimately brings the device to a position such as shown in FIGURE 5, wherein the path between contacts 24, 28 is composed entirely of a low resistance material, while the path between contacts 26, 28 is still composed entirely of high resistance material. Therefore, a waveform such as is designated ,half power in FIGURE 8 has now been developed, with conduction over the full duration, practically speaking, of the positive half-wave and with no conduction whatever during the negative half-wave period of time.

Assuming now that the device is rotated from its FIG- URE 5 to its FIGURE 6 position, the path between contacts 24, 28 will be still composed entirely of low resistance material, whereas the paths between contacts 26, 28 will be in part high resistance and in part low resistance material. By way of example, in FIGURE. 6 the potentiometer has been rotated to a position in which there is a higher ratio of high resistance to low resistance, so that the power output level of the alternating current cycle is approximately two-thirds.

At this time, as will be noted, the meeting line 20 is in registration with the numeral 7 of the scale, and development of the phase angle in the waveform desig nated /3 power in FIGURE 8 is similarly in registration with this numeral on the scale. 7

Further rotation of the potentiometer in the clockwise direction eventually brings it to its other extreme position shown in FIGURE 7 in which there is a path of free conduction between the contact 28 and each of the contacts 26, 24. Therefore, the controlled appliance is now in a full on position as exempified by the lowermost waveform illustration in FIGURE 8.

It will be understood that when the potentiometer has been rotated the full distance from its FIGURE 3 to its FIGURE 7 position, it will be rotated in a reverse direction, counterclockwise in FIGURES 3-7, to return it to its starting or off position shown in FIGURE 3.

FIGURES 10-14 illustrate, schematically, the inventive concept as applied to a potentiometer having a rectilinear rather than a rotary movement. High resistance paths 16a, 18a, are of elongated, straight form, and as in the first form of the invention, would constitute coated or strip materials provided upon an elongated, rectangular base of electrical installation. Rigid with the base would be an operating handle 14a which woud project exteriorly of a housing (not shown) in which the potentiometer is mounted, so as to be shifted back and forth in a straight line by a user between the FIGURE 10, full off position (corresponding to FIGURE 3) and the FIGURE 14 full on position (corresponding to FIG- URE 7). The potentiometer, thus, would be operated in a manner similar to a slide switch between its respective extreme positions.

The resistance paths 16a, 18a meet at a line 20a, so as to abut in end-to-end relation. In wiping contact with the high and low resistance paths is a common line contact 28a and a pair of load contacts 24a, 26a. Contacts 24a, 28a are part of a posttive half-wave control circuit, while contacts 26a, 28a are components of a negative halfwave control circuit.

The contacts are equidistantly spaced, with the contacts 24a, 26a being disposed a distance apart equal to the length of either the surface 16a or 18a. Thus, when the device is in the FIGURE 10 position, the waveform would be that designated full off in FIGURE 8 since all current must flow through high resistance material onl vl hen the device is adjusted in a straight line to the FIG-URE 11 position, there will be a small amount of low resistance material between contacts 26a, 24a, while there would still be only high resistance material between contacts 28a, 26a. The waveform configuration would thus be the minimum on shape shown in FIGURE 8.

FIGURE 11 thus corresponds to FIGURE 4. Similarly,

FIGURES 12, 13, and 14 show positions corresponding to the FIGURES 5, 6, and 7 positions, respectively, of

the rotary potentiometer, producing the half power,"

power, and full on waveforms shown in FIGURE 8. The advantages of the present invention can be readily perceived, in view of the complete elimination of the hysteresis effect and the approximately 50% reduction in voltage change amplification. This is particularly important in view of the fact that in the ordinary house circuit it is not uncommon for variations in voltage to occur. A temporary voltage drop in a particular residential section, even though it may only be momentary, would cause the load, it it has been on its minimum on setting to go off completely, and not come on again until the device is manually turned on by the user.

Contrary to the above, in the present invention the minimum on power output level is virtually zero and in any case it is the same as the turn otf minimum power level. Therefore, the controlled appliance would come on automatically at its previous power level following any interruption of line current.

I claim:

1. A potentiometer comprising:

(a) resistance means including;

(1) a base of electrical insulation; and (2) high and, low resistance paths of electric flow mounted end to end thereon;

(b) a wiper means in contact with said paths and including a first contact and a pair of second contacts, one of said means being movable in respect to the other in a single direction to an infinite number of positions ranging from a full on position in which there is a low resistance path between the first contact and each of the second contacts, to a middle position in which there is a low resistance path be tween the first contact and one of the second contacts, and a high resistance path between the first contact and the other second contact, to a full 01f position in which there is a high resistance path between the first contact and each of the second contacts; and

(c) operating means for shifting at least one of said resistance and wiper means in respect to the other.

2. A potentiometer as in claim 1 wherein said movement is rotary, each of said paths curving about a common center through approximately 180.

3. A potentiometer as in claim 2 wherein said contacts of the wiper means are uniformly angularly spaced approximately apart about said paths.

4. A potentiometer as in claim 3 wherein the second contacts are disposed at opposite sides of the first contact.

5. A potentiometer as in claim 2 wherein said base is of circular configuration and is concentric with said paths, said paths extending along the peripheral area of said base.

6. A potentiometer as in claim 5 wherein said operating means includes a shaft secured to the base and a turn knob for rotating the shaft, said contacts being stationarily mounted adjacent the base in wiping engagement with said paths.

7. A potentiometer as in claim 1 wherein said relative movement of the resistance and wiper means is in a straight line, said paths being aligned longitudinally with one and other along said lines.

8. A potentiometer as in claim 7 wherein said contacts are uniformly spaced along said line.

7 8 9. A potentiometer as in claim 8 wherein, in one ex- 2,764,657 9/1956 Rosenthal 33890 treme position of relative movement of said resistance 2,934,731 4/ 1960 Cotton 323--94 X and wiper means, the second contacts engage the high re- 3,358,151 12/1967 Haase 33889 sistance paths at opposite ends thereof with the first con- 3,320,571 5/ 1967 Webster 33889 tacts midway between the second contacts, and wherein 5 2,850,604 9/ 1958 Rowley 33889 X in the opposite extreme position of relative movement of said resistance and wiper means, the second contacts FOREIGN PATENTS engage opposite ends of the low resistance paths with the 210,523 8/1960 Austrlath first contact midway erebetween LEWIS H. MYERS Primary Examiner e ere c s Cited A. T. GRIMLEY, Assistant Examiner UNITED STATES PATENTS US. 01. X.R. 3,379,567 4/1968 Wrlght 33889 X 33g 150 2,549,389 4/1951 Rosenberg 338150X 15 

